1. Field of Invention
The present invention relates to a method for predicting NOx loading at a DeNOx catalyst and an exhaust system using the same. More particularly, the present invention relates to a method for predicting NOx loading at a DeNOx catalyst by which a NOx amount actually stored in the DeNOx catalyst can be precisely predicted and to an exhaust system which controls a regeneration timing of the DeNOx catalyst and amount of a reducing agent which is injected by using the method.
2. Description of Related Art
Generally, exhaust gas flowing out through an exhaust manifold from an engine is driven into a catalytic converter mounted at an exhaust pipe and is purified therein. After that, the noise of the exhaust gas is decreased while passing through a muffler and then the exhaust gas is emitted into the air through a tail pipe. The catalytic converter purifies pollutants contained in the exhaust gas. In addition, a particulate filter for trapping particulate matters (PM) contained in the exhaust gas is mounted in the exhaust pipe.
A denitrification catalyst (DeNOx catalyst) is one type of such a catalytic converter and purifies nitrogen oxide (NOx) contained in the exhaust gas. If reducing agents such as urea, ammonia, carbon monoxide, and hydrocarbon (HC) are supplied to the exhaust gas, the NOx contained in the exhaust gas is reduced in the DeNOx catalyst through oxidation-reduction reaction with the reducing agents.
Recently, a lean NOx trap (LNT) catalyst is used as such a DeNOx catalyst. The LNT catalyst absorbs the NOx contained in the exhaust gas when the engine operates in a lean atmosphere, and releases the absorbed NOx when the engine operates in a rich atmosphere. The release of the absorbed NOx from the LNT catalyst is called regeneration.
According to a conventional method for regenerating the LNT catalyst, the NOx amount contained in the exhaust gas is predicted based on a driving condition of the engine, the NOx amount stored in the LNT catalyst is predicted from the NOx amount contained in the exhaust gas, and the reducing agents is injected or combustion atmosphere is controlled when the NOx amount stored in the LNT catalyst is larger than or equal to a predetermined amount. In order to perform the conventional method for regenerating the LNT catalyst successfully, the NOx amount stored in the LNT catalyst should be predicted precisely. In addition, in order to predict the NOx amount stored in the LNT catalyst precisely, the NOx amount contained in the exhaust gas should be predicted precisely. A method for precisely predicting the NOx amount contained in the exhaust gas is disclosed in Korean patent application Nos. 10-2010-0115239 and 10-2010-0115238, and a method for precisely predicting NOx amount and NO2 amount remaining at the DeNOx catalyst after previous regeneration is disclosed in Korean patent application No. 10-2010-0121836. Therefore, a method for precisely predicting the NOx amount stored in the DeNOx catalyst will hereinafter be disclosed in this specification.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.